Mechanical properties of heart muscle determine to a great extent the way in which biochemical events in the cell are transduced into muscle tension and ultimately into development of pressure in the heart. Changes in the mechanical properties of the aged heart could account for the observed changes in cardiac performance as determined by a variety of indices. This program uses vibration techniques to measure the components of a cardiac and vascular muscle which determine the overall "stiffness," and measure the age induced effect of the stiffness. Additional studies are purposed to determine the relationship of stiffness to the sarcomere rather than to the gross muscle, and to determine whether the extent to which the myofilaments are activated influences their stiffness properties.